Commissioners of the Springfield Redevelopment Authority approved the change order Tuesday at a special meeting. The Authority owns the station on Frank B. Murray Street and is managing its redevelopment into an intermodal rail and bus transportation hub, a project long championed by U.S. Rep. Richard E. Neal, a former Springfield mayor. The $88.5-million project is state and federally funded.

A six-inch discrepancy in the width of the platform, Platform C, forced a six-month delay in the opening of the platform for passenger use. Union Station will open in January as scheduled, however.

Passengers will access trains from the new terminal by passing through the renovated portion of a tunnel into the current Amtrak lobby and using the currently active boarding platform, Platform D, on the Lyman Street side as they do today.

The tunnel, which dates back to the station's original opening in 1927, will remain open even after Platform C has been renovated so that the rail platforms will be accessible from both Lyman and Frank B. Murray streets. People will be able to walk into the grand concourse and access offices, food service and amenities from Lyman Street and downtown Springfield.

The problem with Platform C is that there is only 5 feet, 6 inches of platform space on either side of the head house. The head house is the building that houses the top of the stairway to the platform and the elevator.

Americans with Disabilities Act standards call for there to be six feet of space between the wall and the edge of the platform.

The city and the Redevelopment Authority first made the delay public at the end of June after they were unable to secure a waiver and were forced to have the platform fixed.

Moskal on Tuesday told Redevelopment Authority Commissioners that the $5 million to fix the problem will come for m the Massachusetts Department of Transportation as part of the state's commitment to the project.

Platform C will be ready by 2018 when the state of Connecticut plans to launch its CTrail Hartford Line commuter service from Springfield through Hartford to New Haven.